I think the difficult part is the combination of all tasks. Each task for its own is more or less manageable but the (successful) integration of all parts is the real challenge.

Project management will be key. How one approaches the task of designing, building, launching, and controlling the rover on the Moon is important. A thoroughly detailed space systems design approach should be used. Focus on the seven classical space subsystems

The Full Prize has a timer of five years. That's enough time to build and fly anything except the ISS

The cut down prize has seven years on it. What would a falcon cost four years from now?

The only thing putting pressure on it is the implosion of the US dollar making the prize worth less and less every year to international competitiors. For people State side there is no rush. With no rush, the cost goes down a fair bit.

despite I don't love (both) Go ogle (you know why...) and "its" prize... a private lunar rover is a great idea (infact, it was/is MY idea...) so (with a little regret) I wish/must talk of it

well, my opinion is that, the #1 problem to solve to win the prize, is not the rover itself (it's an almost simple "RC car") nor the rocket (that will be ready to buy and launch) but everything to do between the earth orbit and the moon soft landing

this is the segment of the mission where the teams risk to fail, then, they need to invest very much money to develop and build a reliable vehicle

The author of that piece makes an irritatingly misleading statement in it:

"Overall, the energy required to soft land a pound on the surface of the moon is hundreds of times greater than that required to lift a pound to an altitude of 62 miles, as Rutan was barely able to do."

When I first read that I took it to mean it took hundreds of times more energy to soft land on the Moon than to get to orbit.
But of course the biggest energy cost is getting to orbit and to escape velocity, not merely making a suborbital launch as Rutan has done.
Also, there have been many small size rockets that have at least achieved Earth orbit haven't there?
Once you have reached Earth's escape velocity what's the energy cost for getting to orbit around the Moon, then making a soft landing?